The present invention relates in general to devices for accurately measuring and checking angles, more particularly to sine bars and their methods o application to the machining of metal parts.
A sine bar is a device for measuring angles to a high degree of accuracy which comprises one or more bars, one of which forms a base or reference point and the other of which extends from the base at the desired angle with the sine bar itself being supported on one end by the base or reference bar and on the other end by a series of gauge blocks which are interposed between a bearing point on the other end and the base or reference surface to form a precise angle. Precisely dimensioned gauge blocks, the reference bar and the sine bar are combined to permit accurate measurement of a predetermined angle by the conventional formula: Sine 0=a/h, where "a" is the height of the interposed gauge blocks and "h" is the length of the hypotenuse formed by the sine bar. This principle is the basis of a prior art sine bar in wide use which comprises a single reference bar for use in conjunction with a flat base, and also of an improved device entitled, "Sine Bar for Lathe Attachment" disclosed in Russian Inventor's Certificate No. 278,353, issued to Kilin G. I. Glukhov on May 8, 1970.
The single element sine bar is commonly used in the prior art cylindrical grinders and other spindle/type machines to set a compound or a head stock accurately to a desired angle.
The problem with the improved model of the type disclosed in the Russian Inventor's Certificate to Glukhov is that the cylindrical body portion of the base member is strictly limited to cylindrical applications and cannot be used on flat surfaces, such as in milling, surface grinding, granite surface plates, and other similar applications. Furthermore, it can only be mounted on spindle type machines by using axially aligned centers at the opposite ends of the bar. This limits the device to specific orientation and thus to specific applications. The Glukhov sine bar is not designed to be mounted on the lathe by use of a collet or chuck at either end of the body which limits its versatility as it must always be mounted between center. Another approach at a compound sine bar is found in U.S. Pat. No. 4,651,435. In this patent, the sine bar comprises a rectangular, elongated base member, projecting from opposite ends of which are cylindrical connector rods. A conforming reference bar is hinged to the base member and has a cylindrical bearing pin fastened beneath one of its ends. When the sine bar is opened to accommodate one or more calibrated gauge blocks, a spring-biased chain keeps the gauge blocks in position between the base member and the bearing pin. A recess is provided in the base member, and permits measurements of small angles. This device is used for setting up a lathe compound to calibrate its angular positions and is also said to be useful for other types of milling and machining operations in which the sine bar rests on a flat surface. The sine bar in this patent is adequate for some purposes but is limited in the angles that it can be used to measure.